SOG Turndown for Tenant Slab 1

[T_Bat]

Hey everyone,

I'm working on a steel framed retail/office building where the interior slab on grade will be the tenant's responsibility. We will still need to provide the wall footings and a band of slab for the light gauge infill walls to attach to. My plan was to show a typical slab turndown onto the wall footing and maybe a 1'-2' wide band of interior slab around the perimeter. The alternative would be to provide a stem wall to support the light gauge. The stem wall is much less concrete but would require additional formwork. The turndown seems like the easiest option but I wanted to be sure I'm not overlooking any ill-affects. Any of you have hesitations using my approach?

Thanks in advance.

 

[DETstru]

If the interior slab on grade will be placed by the tenant at a later date, just do the stem wall.
It leaves an empty space for them to route any plumbing or electrical along the exterior and avoid the need for dowels or a visible construction joint.

 

[XR250]

When i design a turned down slab, I typically rely on the counterweight of a portion of the interior slab to resolve the eccentric loading. If you only have a strip, you would have not have a fat enough guy on the end of your teeter totter. It still can work - just gotta check the numbers.

 

[T_Bat]

Thanks for the insight. I'm leaning toward the turndown with a strip of slab about 3'-4' wide to help with eccentric loading XR250 points out. The architect is fine using this and we should still have plenty off room where the plumbing needs to go.

 

[JAE]

Here's a photo of a turn-down slab method on a project from some time ago - steel framed commercial.

The owner had all sorts of problems with the joint between the first exterior slab strip and the subsequent tenant-provided interior slab.
Essentially the interior slab moved relative to the exterior slab (or visa-versa) and the joint opened up and created problems with floor tile, bumps in carpet, etc.

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[hokie66]

JAE's point is well taken. If the tenant is to provide the slab on ground, leave it to him. Make the external structure independent.

 

[CANPRO]

A little off topic, but I'm curious - is this a common arrangement, having the tenant responsible for the slab? Seems like a very bizzare setup, having everything included but the floor.

 

[jayrod12]

It likely 50/50 around here for that arrangement in CRUs. It allows each tenant to run their required mechanical sub-slab while allowing the developer to "finish" the building.

 

[XR250]

@JAE:

Was that due to slab curling?

 

[JAE]

No - we believe it was mostly settlement in the exterior footing (within allowable ranges) but with any downward movement the piece of slab extending into the building a few feet acts like a wing and the entire gradebeam & "wing" section then rotates with the wing end coming up relative to the interior slab.

They also most likely didn't provide any dowels or other means of resisting vertical differential movements across the joint.

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[T_Bat]

CANPRO - I have not had much experience with this arrangement but for projects involving developers it seems relatively common for the reasons that jayrod12 mentions.

JAE - if properly keyed joints and dowels are used I wouldn't think that the result in your figure would be an issue. Although I feel a little less certain now ha!

 

[jayrod12]

A stemwall removes the possibility of that sort of rotation outright. That would be the way I would go. It can't be much more expensive and then it is done "right".

 

[XR250]

Around here, the developer usually pours the whole slab and they cut it up as needed. It is super efficient :>